The present invention relates to improved aerosolizing devices, particularly but not exclusively for atomizing liquid medicaments to be inhaled, and to a method of constructing such devices.
A wide variety of procedures have been proposed to deliver a drug to a patient. Of particular interest to the present invention are drug delivery procedures where the drug is a liquid and is dispensed in the form of fine liquid droplets for inhalation by a patient. A variety of devices have been proposed for forming the dispersion, including air jet nebulizers, ultrasonic nebulizers and metered dose inhalers (MDIs). Air jet nebulizers usually utilize a high pressure air compressor and a baffle system that separates the large particles from the spray. Ultrasonic nebulizers generate ultrasonic waves with an oscillating piezoelectric crystal to produce liquid droplets. Another type of ultrasonic nebulizer is described in U.S. Pat. Nos. 5,261,601 and 4,533,082. Typical MDIs usually employ a gas propellant, such as a CFC, which carries the therapeutic substance and is sprayed into the mouth of the patient.
The present applicant has also proposed a variety of aerosolization devices for atomizing liquid solutions. For example, one exemplary atomization apparatus is described in U.S. Pat. No. 5,164,740, the complete disclosure of which is herein incorporated by reference. The atomization apparatus comprises an ultrasonic transducer and an aperture plate attached to the transducer. The aperture plate includes tapered apertures which are employed to produce small liquid droplets. The transducer vibrates the plate at relatively high frequencies so that when the liquid is placed in contact with the rear surface of the aperture plate and the plate is vibrated, liquid droplets will be ejected through the apertures. The apparatus described in U.S. Pat. No. 5,164,740 has been instrumental in producing small liquid droplets without the need for placing a fluidic chamber in contact with the aperture plate. Instead, small volumes of liquid are delivered to the rear surface of the aperture plate and held in place by surface tension forces.
Modified atomization apparatus are described in U.S. Pat. Nos. 5,586,550 and 5,758,637, the complete disclosures of which are herein incorporated by reference. The two references describe a liquid droplet generator which is particularly useful in producing a high flow of droplets in a narrow size distribution. As described in U.S. Pat. No. 5,586,550, the use of a dome shaped aperture plate is advantageous in allowing more of the apertures to eject liquid droplets.
One requirement of such aerosolization devices is the need to supply liquid to the aperture plate. In some applications, such as when delivering aerosolized medicaments to the lungs, it may be desirable to regulate the supply of the liquid to the aperture plate so that proper pulmonary delivery of the drug may occur. For example, if too much liquid is supplied, the aerosol generator may be unable to aerosolize fully all of the delivered liquid. On the other hand, if too little liquid is supplied, the user may not receive a sufficient dosage. Further, a metering process may be needed to ensure that a unit dosage amount of the liquid is delivered to the aerosol generator. This may be challenging if the user requires several inhalations in order to inhale the unit dose amount.
The present invention is related to liquid feed systems and methods for delivering liquids to the aerosol generator to facilitate aerosolization of the liquid.